Some skills in EQ2 can be increased by practice. These include Slashing, Ranged, Piercing, etc. All others can only increased by Equipment, Alternate Advancements (AAs), buffs from themselves and other players and in some cases, racial traits. You can view all of these traits in the Persona window (press P).
Ranged/Piercing/Slashing/Parry/etc. Skills: Multiply your level by 6.5. This works out to 520 at level 80.
Double Attack/Ranged Double Attack: 100%.
Double Attack and Ranged Double Attack only affect Auto-attacks.
Casting Haste: 100%.
At 100%, the casting time of spells is half.
Main stats (STR, STA, INT, WIS, AGI): Multiply your level by 15 and add 20 (Level*15 + 20). This works out to 1,220 at level 80.
+Spell Damage Mod, +CA Damage Amt, +Heal Amt: 50% of the base max value of each spell, combat art, or heal.
A spell, combat art, or heal that does 700~1200 can never have a bonus of more than +600, making the new amount 1300~1800.
EQ2 uses a Diminishing Returns system, which means that you are graded on a curve. When you are increasing certain skills, there is a soft cap, beyond which you get less and less benefit from additional skillups. Eventually, you will reach a hard cap, beyond which, there is no further benefit.
Haste/Attack Speed: 200 (which equates to a 125% increase).
Only one Haste item is active, and then multiple Attack Speed items stack on top of that.
DPS: 200 (which equates to a 125% increase).
Spell/Melee/Ranged Crit Chance: 100% (125%)
This effect is scaled down if fighting an enemy of a higher level than you by 5% for each level above you the mob is. If you are level 80 with 50% ranged crit fighting a level 85 mob, you have an effective ranged crit of 35%. Having your primary crit at 125% is recommended to have the highest possible chance of critting. Melee and Ranged Crit affect Combat Arts and Auto-attacks.
Heal Crit Chance: 100%.
Due to rounding errors, it is advisable to have 105%.
Mitigation: Multiply level by 150. This calculates to 12,000 or 75% at level 80.
work in progress part (starting from a post by SageGaspar):
>> Gungo wrote:
>> crit bonus isnt garaunteed like base its a spread of max+1 to Max +(.3+ crit bonus)
That's only true until your min*crit multiplier is bigger than max+1, and then it's just a straight up percent increase. For a lock most spells, depending on your spell damage, have something like a 1.75 point to break even and all but one I believe by 2.0.
Just as an example to illustrate if a spell does 1000-1500 and you have the base 1.3 crit its damage range is 1501-1950 weighted more heavily towards the 1501 end.
If you have 1.5 crit mod its damage range is now 1501-2250. This is the breaking point where crit mod has now reached its maximum effectiveness. Everything after this is straight damage multiplier.
If you have a 2.0 crit mod the damage range becomes 2000-3000. You will not see a 1501 hit ever.
The difference between stacking this and base damage? Base damage is hard capped, and base damage raises the amount of spell damage you can add if you're capped already, otherwise you'd just stack whichever one was lower.